Re: Oil Pressure Mushroom

Posted: Sat May 05, 2018 8:14 am

by roger lee

The newer style mushroom is an option. Rotax still uses the ball bearing in new engines. Nothing wrong with changing the oil pressure plug screw, spring and mushroom. If you replace the plug the spring also needs to be replaced. If you just get rid of the ball bearing the spring needs to be replaced. If you are swapping out the old plug screw and want the mushroom replace all three parts.

Oil pressure shims should NEVER be used without a mechanical gauge confirmation of the true oil pressure. You almost never see a true low oil pressure. It is usually a bad sending unit, poor ground, reduced radius oil supply hose, wrong sensor type selected if you have a digital instrument or just a bad connection. These all must be ruled out first. I've had several come to the shop that swore it was low oil pressure. They put a shim in and then the pressure would be up in the 80's.

Mechanical gauge confirmation first is a must.

Re: Oil Pressure Mushroom

Posted: Sat May 05, 2018 8:58 am

by FastEddieB

roger lee wrote:The newer style mushroom is an option. Rotax still uses the ball bearing in new engines.

That surprises me.

Is there then a 1,500 hr TBO on a factory new engine until the ball bearing and associated parts are replaced?

Doesn’t make sense they would not ship engines without the latest parts. I wonder what the logic is.

Re: Oil Pressure Mushroom

Posted: Sat May 05, 2018 9:09 am

by 3Dreaming

FastEddieB wrote:

roger lee wrote:The newer style mushroom is an option. Rotax still uses the ball bearing in new engines.

That surprises me.

Is there then a 1,500 hr TBO on a factory new engine until the ball bearing and associated parts are replaced?

Doesn’t make sense they would not ship engines without the latest parts. I wonder what the logic is.

The ball is not required to be replaced as part of the upgrade to extend the TBO, it is optional if you have fluctuating oil pressure. IMO the swap out of parts is nothing more than a way to determine if the engine has the extended TBO.

Re: Oil Pressure Mushroom

Posted: Sat May 05, 2018 9:32 am

by FastEddieB

Last two post definitely change my calculus.

Reconsidering spending $50 or $60 for no obvious benefit.

I was pretty sure I had read that part had to be replaced to extend the TBO.

Edited to add: I see Roger says in that same post that very little oil is lost, a no purge should be necessary if that’s all that’s done.

Re: Oil Pressure Mushroom

Posted: Sat May 05, 2018 11:49 am

by TimTaylor

I would just do it and not look back.

Re: Oil Pressure Mushroom

Posted: Sat May 05, 2018 4:02 pm

by drseti

On every plane I've upgraded to the 2000 TBO, I replaced merely the spring and cap (not the ball). I've never found the mushroom to be necessary, although I do keep one in stock just in case. But it is important to check the engine s/n to see if it's eligible for the upgrade. (Anything with a crankcase s/n > 06.0010 should be.)

Re: Oil Pressure Mushroom

Posted: Sat May 05, 2018 4:46 pm

by roger lee

To extend TBO it's just the plug screw and spring. The mushroom is optional and no purge is necessary because of the tiny amount of oil lost. The ball bearing has been known to cause chattering and slight oil pressure fluctuations due to the rounded surface tension on the ball and its seat. The mushroom has a hole in it and a sharper curve plus the long stem to help hold the spring straight and not bend. The spring also was involved in oil fluctuation because with the old short plug screw because it would let the spring rub on the housing wall. If you want to keep the ball bearing no big sweat. Rotax years ago came out and said it was more concerned with volume over pressure. So I would rather see 45-50 psi over 65 psi. The way the plug screw, spring and ball bearing work is when oil is forced through the pump and on its way out the other side it creates a pressure. The spring is tensioned to maintain a certain pressure and when the pressure exceeds the outlet pressure the ball bearing / spring compress down and allow oil to go back into the inlet side of the pump. If there is a Rotax engine that needs a shim then you better confirm that with a separate mechanical gauge and better just fix the cause of the low pressure. I would consider something below 40 psi on every single flight something that should be looked at. 45+ psi is no big deal. Pressure is a range and not an absolute number.Wrong oil types, reduced radius hose, reduced radius fittings, oil tank bottom plate upside down and low oil level can affect the pressure. Once in a great great while and oil pump has an issue.

Re: Oil Pressure Mushroom

Posted: Sat May 05, 2018 4:50 pm

by FastEddieB

I don’t have my engine serial # handy - will check when next at the hangar.

I read somewhere of there are no washers underneath the cylinder head bolts, it’s the new, eligible design. Mine does not have those washers, if that means anything.